Abstract

Free cortisol as measured in saliva increased markedly following awakening. This study investigated, with 11 adults (mean age 21.7 yrs) whether the awakening cortisol response can be generated in the middle of nocturnal sleep. In a within subject design, salivary cortisol response was measured under three different awakening conditions: at normal morning awakening time; awakening 4 hrs prior to normal awakening time; and awakening the following morning after interrupted sleep. The overall main effect was a linear increase in free cortisol following awakening with no significant interaction with awakening condition. Cortisol levels differed by awakening condition. The two morning awakening conditions were comparable but values were lower for night awakening. It is concluded from the data that there is a clear free cortisol response to awakening for both nocturnal and morning awakening although the absolute levels produced are lower for nocturnal awakening when basal cortisol is low. Nocturnal interruption of sleep did not affect the subsequent morning response.